Navigation systems access digitized maps of the traffic-route network or road network as the basis for vehicle navigation. These maps are not standardized, so that in response to maps from different producers, deviations in the digitized map information may come about.
In a dynamic navigation that is usual these days, the navigation system checks the route that has already been computed, based on received traffic data on the current traffic position, or it is computed again while taking into account the changed traffic situation. Traffic data are usually allocated to certain route sections of the traffic-route network, in order to make the localization possible. The navigation system now has uniquely to localize the route section of localized in the map available to it, in order to be able to take into consideration the received traffic message in the route computation. This localization is also designated as referencing.
In the referencing of parts of the traffic-route network, coordinates of (shape) points of the route sections are essentially coded on an encoder side, which has a first digitized map, and transmitted to the decoder system, together with certain attributes, which accesses a second digitized map. The corresponding route section is identified on the decoder side, with the aid of these coordinates and attributes. These coordinates that are to be transmitted are selected partially to be equidistant and partially with the aid of certain algorithms, such as the Douglas-Peuker algorithm. A correlation with the data of the receiver map is then computed for the decoding, the transmitted coordinates being shifted within a certain framework. In the case of a maximum, a correct shifting is assumed, which is verified with the aid of the attributes. Consequently, a unique identification of the route section has been made possible.
The decoding is often insufficient without the use of further attributes, since, for example, parallel roadways cannot be distinguished. But even when further attributes are used, such as the direction of travel and the like, it often happens that a unique maximum cannot be determined. In addition, routing through the correlated points increases the runtime of the decoder. This is required, however, since, during the correlating of the points in the first step, the topology cannot be taken into account. As a result, it may happen that points which are really adjacent, turn up on different roads of the road network. Furthermore, on account of the many points that are to be transmitted, the volume of data rapidly becomes quite large, but for correct identification, a plurality of points is indispensable in the case of some roads.